feat(skills): 新增 Skill 调用统计（账本 + 页面总览/详情）

后端：
- 新表 skill_usage（无外键，任务/会话删除后统计保留），一次 Skill()
  调用记一行，只记维度不记 args 正文；含 found 标记未命中调用
- 用 RunInfo 经 ctx 把 task/exploration/intent/session 传到工具装配层，
  在 Skill meta-tool 外包一层做埋点（可记 args 长度与不存在的 skill）
- fsListSkills 返回附带调用次数/覆盖任务/最近调用；新增
  GET /api/skills/missing 与 GET /api/skills/{name}/usage

前端（/system/skills）：
- 树节点显示调用次数 badge；目录优先排序 + 子项缩进错开一级
- 空态改为技能库总览（指标卡 + 调用排行 + 最近/未使用）
- 选中 skill 的详情面板改为响应式左右分栏（配置在左、统计在右，
  窄屏回落上下），含最近调用明细与未命中缺口清单

Claude-Session: https://claude.ai/code/session_01BNN7npEJs4X6LfTtgniMd8

server/assembly.go

@@ -137,7 +137,11 @@ func wireAgentAugment(pg *db.DB, skillDir string, hostTools func() ([]actool.Cor
 				}
 				return actool.RenderDeferredToolsBlock(reveal)
 			}
-			extra = append(extra, reg.Tool())
+			// Attribution for the usage ledger: ToolAugment only gets (ctx, agentKey),
+			// so the run's task/session ids ride in on the ctx (agent.RunInfo). Read it
+			// once here — this closure is rebuilt per run, so the captured value always
+			// belongs to this run.
+			extra = append(extra, meterSkillTool(reg.Tool(), pg, reg, a.Key, agent.RunInfoFrom(ctx)))
 		}
 
 		// host tools (traffic / orchestration / custom) — added to every agent's base;

server/server.go

@@ -776,6 +776,8 @@ func (s *Server) Handler() http.Handler {
 	mux.HandleFunc("POST /api/skills", s.fsCreateSkill)
 	mux.HandleFunc("POST /api/skills/upload", s.fsUploadSkill)
 	mux.HandleFunc("DELETE /api/skills/{name}", s.fsDeleteSkill)
+	mux.HandleFunc("GET /api/skills/missing", s.fsMissingSkills)   // 未命中(想调但不存在)的 skill 名
+	mux.HandleFunc("GET /api/skills/{name}/usage", s.fsSkillUsage) // 单个 skill 的最近调用
 	mux.HandleFunc("PUT /api/skills/{name}/meta", s.fsUpdateSkillMeta)
 	mux.HandleFunc("POST /api/skills/{name}/dirs", s.fsCreateDir)
 	mux.HandleFunc("GET /api/skills/{name}/files", s.fsListFiles)

server/server_mgmt.go

@@ -897,6 +897,12 @@ type skillFileNode struct {
 	Compatibility string   `json:"compatibility,omitempty"`
 	MCPs          []string `json:"mcps,omitempty"`
 	Files         []string `json:"files"`
+	// Usage ledger (db/skill_usage.go). Calls is 0 and LastUsed nil for a skill that
+	// was never invoked — the ledger only has rows for skills agents actually loaded.
+	Calls    int        `json:"calls"`
+	Tasks    int        `json:"tasks"`
+	Agents   []string   `json:"usage_agents"`
+	LastUsed *time.Time `json:"last_used,omitempty"`
 }
 
 func (s *Server) fsListSkills(w http.ResponseWriter, r *http.Request) {
@@ -915,13 +921,28 @@ func (s *Server) fsListSkills(w http.ResponseWriter, r *http.Request) {
 		writeErr(w, 500, err.Error())
 		return
 	}
+	// Usage is best-effort decoration: a ledger read failure leaves the counts at
+	// zero rather than failing the skill list itself.
+	statBySkill := map[string]db.SkillStat{}
+	if s.m.pg != nil {
+		stats, err := s.m.pg.SkillStats()
+		if err != nil {
+			log.Printf("[skills] 读取调用统计失败: %v", err)
+		}
+		for _, st := range stats {
+			statBySkill[st.Skill] = st
+		}
+	}
 	nodes := []skillFileNode{}
 	for _, e := range entries {
 		if !e.IsDir() {
 			continue
 		}
 		dirName := e.Name()
-		node := skillFileNode{Name: dirName}
+		node := skillFileNode{Name: dirName, Agents: []string{}}
+		if st, ok := statBySkill[dirName]; ok {
+			node.Calls, node.Tasks, node.Agents, node.LastUsed = st.Calls, st.Tasks, st.Agents, st.LastUsed
+		}
 		if meta, ok := metaByDir[dirName]; ok {
 			node.Description = meta.Description
 			node.License = meta.License
@@ -937,6 +958,42 @@ func (s *Server) fsListSkills(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, 200, map[string]any{"skills": nodes})
 }
 
+// fsSkillUsage returns one skill's recent invocations, newest first (detail panel).
+func (s *Server) fsSkillUsage(w http.ResponseWriter, r *http.Request) {
+	pg := s.pg(w)
+	if pg == nil {
+		return
+	}
+	name := r.PathValue("name")
+	if !validSkillName(name) {
+		writeErr(w, 400, "非法 skill 名")
+		return
+	}
+	limit, _ := strconv.Atoi(r.URL.Query().Get("limit"))
+	calls, err := pg.RecentSkillCalls(name, limit)
+	if err != nil {
+		writeErr(w, 500, err.Error())
+		return
+	}
+	writeJSON(w, 200, map[string]any{"calls": calls})
+}
+
+// fsMissingSkills lists skill names agents asked for that do not exist — the gap
+// list, i.e. which procedures are worth writing next.
+func (s *Server) fsMissingSkills(w http.ResponseWriter, r *http.Request) {
+	pg := s.pg(w)
+	if pg == nil {
+		return
+	}
+	limit, _ := strconv.Atoi(r.URL.Query().Get("limit"))
+	missing, err := pg.MissingSkillStats(limit)
+	if err != nil {
+		writeErr(w, 500, err.Error())
+		return
+	}
+	writeJSON(w, 200, map[string]any{"missing": missing})
+}
+
 // cleanStrs trims each string and drops empties.
 func cleanStrs(in []string) []string {
 	out := make([]string, 0, len(in))